The condensation reaction of an olefin or a mixture of olefins to form higher molecular weight products is widely known and practiced. This type of condensation reaction is referred to herein as an oligomerization reaction or process, and the products are low molecular weight oligomers which are formed by the condensation of up to 12, typically 2, 3 or 4, but up to 5, 6, 7, or even 8 olefin molecules with each other. “Oligomerization” refers to a process for the formation of oligomers and/or polymers. Low molecular weight olefins (such as, for example, ethylene, propene, 2-methylpropene, 1-butene and 2-butenes, pentenes and hexenes) may be converted by oligomerization over, for example, a solid phosphoric acid catalyst (commonly referred to as “sPa” catalyst) or a molecular sieve catalyst (e.g., a zeolite catalyst), to an oligomer product.
Oligomer products are valuable components of high-octane gasoline blending stock that may be used or blended into a distillate type liquid fuel or as a lubricant, or as a starting material for the production of chemical intermediates and end-products. Such chemical intermediates and end-products include high purity hydrocarbon fluids or solvents, alcohols, detergents/surfactants, and esters such as plasticizer esters and synthetic lubricants.
A number of catalysts may be used in such oligomerization processes. For example, industrial oligomerization reactions employing molecular sieve catalysts are generally performed in a plurality of tubular or chamber reactors, similar to those processes employing sPa catalysts. With sPa catalysts, the pressure drop over the catalyst bed(s) increases gradually over the duration of the run, due to coking and/or swelling of the catalyst pellets and the reactor run is typically terminated when a maximum allowable pressure drop over the reactor is reached. Molecular sieve catalysts do not show pressure drop increases similar to sPa catalysts. Oligomerization reactors using molecular sieve catalysts are therefore characterized by longer reactor run lengths and are typically decommissioned when the catalyst activity has dropped to an unacceptably low level. With these catalysts, the reactor run length that can be achieved is therefore much more sensitive to compounds, impurities, or contaminants in the feedstreams that deactivate the catalyst, such as catalyst poisons.
The art is replete with endeavors that attempt to remove or minimize levels of contaminants or impurities that adversely affect catalyst life and activity. For example, strong bases, such as the proton bases or Bronsted bases, are known poisons for many of the oligomerization catalysts that are acidic, for example, molecular sieve catalysts. Such bases in hydrocarbon streams are often nitrogen containing compounds, such as amines and amides, and they are typically removed from feedstreams for oligomerization reactions and other hydroprocessing reactions. Such organic nitrogen-containing Bronsted bases are characterized by at least one hydrogen atom bound to the nitrogen atom and are known proton acceptors. Other organic nitrogen components do not have any hydrogen atoms bound to the nitrogen and the nitrogen atom may have three bonds to 1, 2 or 3 surrounding carbon atoms. These nitrogen atoms however still have a free electron pair and therefore can still act as a base, termed a Lewis base. Lewis bases are known to be weaker bases as compared to Bronsted bases and therefore are sometimes considered less problematic to acid catalyzed processes.
Numerous attempts have been made to treat feedstreams or feedstocks prior to undergoing hydroprocessing or petrochemical reactions. See, for example, U.S. Pat. No. 4,973,790 (disclosing a process for oligomerization of C2 to C10 olefins over a zeolite catalyst comprising a feed pre-treatment step to remove basic nitrogen compounds, for example, amines such as di-ethanol-amine); U.S. Pat. No. 5,675,043 (disclosing processes for treating a hydrocarbon blend containing nitrogen-containing compounds with a solvent having a Hansen polar solubility parameter to effect removal of a portion of said nitrogen-containing compounds therefrom); U.S. Patent Application Publication No. 2002/103406 (disclosing a process for oligomerizing an olefin originating from an oxygenate to olefin process using a nickel based catalyst, the olefin stream having a low nitrogen content, as low as 0.3 ppm by weight); U.S. Patent Application Publication No. 2004/0097773 (disclosing a process for oligomerizing isobutene wherein feedstocks have been treated to remove nitrogen components, for example, acetonitrile and N-methyl-pyrrolidone); U.S. Pat. Nos. 7,205,448, 7,744,828, and U.S. Patent Application Publication No. 2007/0213575 (disclosing the removal of nitrogen compounds, including a number of Lewis base compounds such as nitriles, for example, acetonitrile, N-methyl-pyrrolidone, morpholines such as N-formyl morpholine, pyridine and/or quinoline, from feedstreams); Nagai et al., Isolation of Nitrogen-containing Heterocyclic Compounds Contained in Coal Tar Absorption Oil Fraction with Solvent Extraction, Sekiyu Gakkaishi (Journal of the Japan Petroleum Institute), 43 (5), 339-345 (2000) (disclosing using aqueous solutions of methanol or tetrahydrothiophene-1,1-dioxide (sulfolane) to remove heterocyclic compounds containing nitrogen atoms from coal tar oil absorption oil fractions); and SU 1086006 (disclosing using a metal chloride such as NiCl2 in an organic solvent such as propylene carbonate or dimethylsulfoxide or dimethylformamide to remove nitrogen compounds from petroleum products by complexing the metal chloride with the nitrogen compounds). Other background references include U.S. Patent Application Publication Nos. 2005/0137442, 2005/0152819, 2008/0312484, U.S. Pat. Nos. 4,153,638, 5,569,790, 6,160,193, EP 1 002 852 B, GB 1,131,989, WO 2000/71494, and WO 2012/078218.
As can been seen, much effort has been made directed to removing impurities and contaminants from feedstreams where much of the work has been focused on removing alcohols, ketones, organo sulfur compounds, such as, for example, sulfides and thiols or mercaptans, nitrogen containing compounds, such as, for example, nitriles, pyrroles, amines, amides, imides, indoles, cyanates, pyridines, pyrrolidones, and combinations thereof. Although these contaminants and impurities remain important to the efficiency of the oligomerization reaction, little work has been focused regarding ammonia, either alone or with other compounds, and its ability to reduce the efficiency and life and the oligomerization catalyst.
In particular, C3 olefin containing feedstreams create unique challenges with respect to ammonia as compared to other feedstreams such as C4 olefin containing feedstreams. For example, pure propylene has a boiling point of −47.6° C., pure propane has a boiling point of −42° C., and pure ammonia has a boiling point of −33.3° C. Any Ammonia present in a stream containing C3 and C4 molecules (such as isobutane, butane, isobutene, and butenes that have a range of boiling points between −11.7° C. and +3.7° C.), that is fractionated to a C3 rich stream and a C4 rich stream will fractionate with the C3 rich stream. If there is any acetonitrile present (boiling point 81° C.), in the C3/C4 stream, once fractionated, the acetonitrile will fractionate with the C4 rich stream. Once the separation of the C3 rich stream and C4 rich stream is completed, the challenges associated with ammonia in the C3 rich stream and acetonitrile in the C4 stream are different. This is due to the different type of bases (i.e., Bronsted bases versus Lewis bases) and the different properties of the hydrocarbon stream containing the different nitrogen species. In the fractionation of the C3 rich stream from the C4 rich stream, it is not possible for ammonia to fractionate with the C4 rich stream, or the acetonitrile to fractionate with the C3 rich stream, due to large differences in relative boiling points. Thus, C3 rich feedstreams pose different challenges from past endeavors to remove other nitrogen species from hydrocarbon feedstreams.
One source of such feedstreams include C3 olefin containing Liquefied Petroleum Gas (“LPG”) from refinery sources such as Fluidized Catalytic Crackers (“FCC”). Normally, these streams are treated to remove sulphur containing compounds (such as, for example, hydrogen sulphide and mercaptans) These LPG streams may also contain contaminants such as basic nitrogen compounds (including but not limited to ammonia, amines (such as, for example, monoethanolamine), acetonitrile, and propionitrile. As a solution, amine treating and caustic scrubbing are used to remove the many of the sulphur containing compounds.
However, these processes are not effective to remove basic nitrogen compounds such as ammonia. Thus, oligomerization units using acidic catalysts as described above will be vulnerable by the presence of these basic nitrogen compounds. Ammonia is a common nitrogen containing compound in feedstreams and abundantly available, especially in C3 containing feedstreams. Thus, cost effective removal of these nitrogen containing compounds is essential for manufactures of oligomers to ensure economic catalyst performance.
One solution proposed to removing these nitrogen containing compounds such as ammonia is washing olefin feedstreams with water in various contact devices prior to oligomerization. See, for example, U.S. Pat. No. 7,569,741 (suggesting the use of a washing agent including water in a purification process for feedstocks, predominantly aromatic feedstocks, to remove polar impurities). Many oligomerization catalyst suppliers recommend using acidified water. This solution may also be found in the art. See, for example, U.S. Pat. No. 4,973,790 (suggesting the removal of nitrogen containing compounds with water washing, preferably with acidified water) and U.S. Pat. No. 5,414,183 (suggesting the removal of residual products using water washing where the water is usually acidified with a mineral acid to maintain a pH at an optimum level below 7). U.S. Patent Application Publication No. 2007/0213575 and U.S. Pat. No. 7,989,668 disclose treating an olefin-containing hydrocarbon stream comprising an organic nitrogen-containing Lewis base to thereby lower the concentration of the organic nitrogen-containing Lewis base in the olefin-containing hydrocarbon stream and subsequently contacting the treated olefin-containing hydrocarbon stream with a molecular sieve oligomerization catalyst. The reference states that a preferred extraction step is a water wash, because of the ready availability of suitable wash water. It is preferred that the pH of the wash water is not too high, such as at most 9.5, but preferably it is at most 9 and more preferably at most 8. Most preferably the water is slightly acidic, with a pH below 6.5, 6, 5 or even 4. However, the '668 patent only exemplifies a butene stream containing 90% normal butenes that would not present the same challenges with respect to ammonia and C3 containing streams as explained above. As such, the '668 patent's treatment step is directed to the removal nitriles such as acetonitrile.
Egloff et al., Polymerisation with Solid Phosphoric Acid Catalyst, Proceedings of Third World Petroleum Congress, Section IV, pages 202-214, (1951) discloses that ammonia and amines, being basic in character, will act to neutralize the acidic catalyst, thereby rendering it inactive. The chemical reaction between these basic substances and the acid in the catalyst causes softening and gradual disintegration. These substances can be eliminated by washing the feed with water in a countercurrent system. It further teaches that where basic nitrogen compounds are known to be present in large quantities, the most effective removal is obtained by the use of water having a pH controlled by sulfuric acid injection. See also, McMahon et al., Polymerization of Olefin as a Refinery Process, Advances in Petroleum Chemistry and Refining, Vol. 7, Chapter 5, pages 285-321, (1963) (“Efficient washing of feed with slightly acidified water is required to maintain this degree of purity.”)
With respect to washing with acidic water, in order to meet the recommended pH levels on the inlet and outlet of the contacting device, the provision of acid injection and a pH control is required to maintain optimum water pH. Acid injection facilities are costly and present process control challenges as the pH response to changes in acid injection is not linear. Additionally, the presence of acid either corrodes equipment and facilities and makes materials selection to mitigate against potential acid corrosion challenging as well.
Thus, many catalysts and their respective catalyst lives may be profoundly influenced by contaminants, such as, for example, ammonia and other contaminants or impurities found in feedstocks. Therefore, there remains a long-standing need to address the problems associated with contaminants in feedstreams, in particular, ammonia, in C3 olefin containing feedstreams.